Research On The Configuration And Stability Of The Wave-shaped Free-form Grid Shell

Free-form space grid structures,with the predominant architectural expressiveness and strong visual impact,which have become one of the prevailing trends of the development of spatial structures,have been developed rapidly and used widely in recent years.However,there still remains two key issues to be solved in the design of such structures.One is the hardness of the realization of geometric features based parametric modeling and the low design efficiency for it is difficult to classify the free-form space grid structures by their geometric features while pursuing flexible and liberalized architecture modeling.The other is the lack of researches in terms of the stability performance of free-form grid structures,especially the dynamic stability,due to the different stability performance between the "formative structure" and the traditional spatial structure when under static and dynamic loads.By integrating the characters of deep-sea scallops into the reticulated spherical shell,one class of the wave-shaped free-form grid shell is proposed in this dessertation.Non-uniform rational B-splines is used as the expression means.The geometric features and the characteristic parameters of this structure are elaborately summarized.And a series of morphological analysis and stability research of this structure are carried out in detail.For morphological analysis,the parametric configuration of the wave-shaped free-form grid shell is realized by extracting the geometric characteristic parameters of the structure with the method of visual Programming in the Grasshopper platform.The parameterized mesh of multiple grid forms is achieved through iso-parametric curve division,which exactly verifies the feasibility of the method of parametric modeling.The method of feasible direction algorithm equipped with Multi-Start optimizing function,which selects the overall strain energy and the buckling eigenvalues as the objective function and sets the point coordinates as the design variable,is adopted in the software Hypermesh and Optistruct to achieve the multiple-object optimum of the free-form space grid structure.The results indicate that this method is of high efficiency and good optimize result.Only a single adjustment of geometric parameters can largely increase the overall stiffness and stability of the structure.As for stability,nonlinear full-range analysis under static loading and nonlinear time-history dynamic analysis under the seismic motion of the wave-shaped free-form grid shell are analyzed in the software ANSYS.Based on the analises,mechanism of instability of the wave-shaped free-form grid shell has been revealed.The effects of grid forms,geometric parameters,initial geometric imperfection and asymmetric distribution of live load on the structural static stability are firstly addressed in this paper.The wave characteristics are enlarged step by step on the basis of spherical shell trait aiming at highlighting the different instability mechanisms caused by wave characteristics alteration.Dynamic responses and failure modes of the structure are dealt with under distinct wave characteristics,earthquake direction and seismic waves.Key findings of the study involve that Kiewitt grid possesses better static and stability characteristic compared with rib-patterned grid,rib-loop tilted bar grid,diagonal quadrilateral grid.It is found that there mainly exist three instability modes of the structure when under full span of static load,namely torsional buckling,vertical overall instability and horizontal overall instability,which varies with the geometrical parameter.Geometric parameters and initial geometric imperfection have a great impact on the static stability of the structure while the asymmetric distribution of live load makes a relatively minor difference.It is also found that and the structural failure mode varies with wave characteristics.The ultimate bearing capacity under static loading and the seismic motion decreases first and then increases.Horizontal seismic makes more significant effects than vertical seismic.It is more reasonable to take the three-directional earthquake action into consideration.In engineering design,it is considerate to select multiple kinds of seismic waves when analyzing dynamic stability of the structure for the reason that dynamic stability critical load of the structure alters when under different seismic waves.